Fractionated Morse Cipher

Encode and decode the Fractionated Morse cipher. The message is first written in Morse with a single x between letters and a double x between words, the dot-dash-x stream is then read three symbols at a time, and each of the 26 possible groups is replaced by a keyed cipher letter. Mix the alphabet with a keyword, follow the live letters-to-Morse-to-trigraph working, and copy, download, or share the result. Everything runs in your browser.

Keyword

The keyword mixes the 26 cipher letters: its unique letters come first, then the rest of the alphabet, and that order is matched against the 26 trigraphs. Leave it blank for the plain A–Z table. Both sides must use the same keyword.

Plain text

Cipher text

Enter text above to see the result here.

Trigraph → letter table

...

..-

..x

.-.

.--

.-x

.x.

.x-

.xx

-..

-.-

-.x

--.

---

--x

-x.

-x-

-xx

x..

x.-

x.x

x-.

x--

x-x

xx.

xx-

How to use Fractionated Morse Cipher

1
Choose encode or decode
Pick Encode to turn plain text into Fractionated Morse cipher text, or Decode to turn cipher text back into plain text.
2
Set a keyword (optional)
Enter a keyword to mix the cipher alphabet, or leave it blank to use the plain A–Z table. Both sides must use the same keyword to match.
3
Type or paste your text
Enter your message and it is converted as you type. When encoding, the steps panel shows each letter over its Morse, then the stream cut into trigraphs with the cipher letter under each.
4
Read the trigraph table
Open the trigraph table to see all 26 three-symbol groups with the cipher letter each maps to, and any keyword letters highlighted.

5
Copy, download, or share
Copy the result, download it as a text file, or share a link that reopens the tool with your exact text and keyword ready to go.

Understanding the Fractionated Morse Cipher

What is the Fractionated Morse cipher?

The Fractionated Morse cipher takes ordinary Morse code and wraps a second, keyed layer around it so that the familiar dots and dashes never appear in the finished message. It belongs to a family of hand ciphers popularised by the American Cryptogram Association, and it is a favourite in puzzle hunts, geocaching, and capture-the-flag challenges because it looks like a plain letter substitution while hiding a Morse skeleton underneath.

The word fractionated describes the trick at its heart. After the message is turned into Morse, the stream of dots, dashes, and separators is chopped into fixed groups of three and each group is replaced by a single cipher letter. Because three Morse symbols almost never line up neatly with one plaintext letter, every cipher letter ends up carrying fragments of two or three neighbouring letters. That blending is what erases the tell-tale rhythm of Morse and flattens the letter frequencies that would otherwise give the message away.

Three symbols, twenty-six groups

To make Morse into a single unbroken string you need a separator. Fractionated Morse uses the letter x: a single x between letters and a double xx between words. So the message now uses just three symbols — dot, dash, and x — and nothing else.

Read three of those symbols at a time and there are 3 × 3 × 3 = 27 possible groups. One of them, xxx, can never occur, because a run of separators is at most a double xx between words. That leaves exactly 26 possible groups — the same as the number of letters in the alphabet. That neat coincidence is the whole reason the cipher works: every group of three can be assigned its own cipher letter with none left over and none missing.

The keyword and the substitution table

The 26 three-symbol groups, called trigraphs, are always listed in the same fixed order, from dot-dot-dot up to x-x-dash. What changes is the row of cipher letters written beneath them. With no keyword the letters are simply A, B, C, … in order, so dot-dot-dot becomes A, dot-dot-dash becomes B, and so on. The live table above shows this mapping and updates the moment you type.

A keyword mixes that row of letters exactly like a keyed simple-substitution alphabet. The keyword's unique letters are written first, in order and without repeats, and the rest of the alphabet follows. The keyword MORSE, for example, produces the cipher alphabet MORSEABCDFGHIJKLNPQTUVWXYZ, so dot-dot-dot now becomes M instead of A. The keyword is the shared secret: sender and receiver must use the same one, and the highlighted cells in the table mark the letters that came from it.

How the Fractionated Morse cipher works

Encoding runs in three moves. First, write the whole message in Morse, putting one x between letters and two between words. Second, if the resulting string is not a multiple of three symbols long, pad the end with x until it is — padding with x rather than a dot or dash matters, because a stray dot would later be read back as a spurious letter. Third, slice the string into groups of three and replace each group with its cipher letter from the keyed table.

The power of the cipher is in that second slicing. A single plaintext letter, once turned into Morse and joined to its neighbours with separators, is spread across several groups of three, and each group also borrows symbols from the letters on either side. Recovering one plaintext letter therefore means reconstructing the surrounding Morse as well, which is exactly what defeats the simple letter-counting attacks that break a plain substitution cipher. The steps panel above lays this out live: the top row pairs each letter with its Morse, and the bottom row shows the stream cut into trigraphs with the cipher letter under each.

A worked example

Take the distress call SOS with no keyword. In Morse, S is dot-dot-dot and O is dash-dash-dash, so SOS becomes the stream dot-dot-dot x dash-dash-dash x dot-dot-dot. That is eleven symbols, which is not a multiple of three, so a single x is added to the end to make twelve.

Now read the twelve symbols three at a time. The groups are (dot-dot-dot), (x dash-dash), (dash x dot), and (dot-dot x). With the plain A–Z table those four trigraphs map to A, W, P, and C, so SOS encrypts to AWPC. Notice how the second and third cipher letters straddle the boundaries between the original S, O, and S — that straddling is the fractionation at work. Add a keyword, and the same four trigraphs land on four different letters while still decrypting back to SOS.

Decoding a Fractionated Morse message

Decoding simply runs the three moves backwards. Each cipher letter is looked up in the table to recover its trigraph, the trigraphs are joined back into one long dot-dash-x string, and that string is split on the separators — a single x ends a letter, a double xx ends a word. Reading each run of dots and dashes back through the Morse table rebuilds the original text. Any x padding that was added during encoding sits harmlessly at the end and disappears, so a message that was encoded with this tool always decodes back exactly.

To decode correctly you must use the same keyword that was used to encode; a different keyword pairs the trigraphs with the wrong letters and the Morse comes out as nonsense. Because only letters and digits have Morse codes, any punctuation or other symbols in the original message were dropped during encoding and will not return. Spaces between groups of cipher letters are ignored on decode, so it does not matter whether the cipher text was written solid or in tidy blocks of five.

History, uses, and security

Fractionated Morse is one of a number of Morse-based pencil-and-paper ciphers — alongside Morbit and Pollux — that were catalogued and kept alive by the American Cryptogram Association for recreational cryptanalysis. They reward solvers who can spot the hidden Morse structure, and they remain a staple of cipher challenges precisely because the fractionation step makes them more interesting than a straight substitution.

By modern standards the cipher is not secure. The fractionation defeats naive frequency analysis, but the underlying Morse imposes strong statistical patterns, and a known or guessed keyword, or simply enough cipher text, lets a determined solver or a computer recover the message. Treat Fractionated Morse as a puzzle and a teaching tool — a vivid demonstration of how combining encoding with substitution strengthens a cipher — and never as a way to protect real secrets. For genuine confidentiality, always use a modern, peer-reviewed algorithm such as AES.

Frequently asked questions

What is the Fractionated Morse cipher?

It is a hand cipher that hides Morse code inside a letter substitution. The message is written in Morse with x separating letters and xx separating words, the dot-dash-x stream is read three symbols at a time, and each of the 26 possible three-symbol groups is replaced by a cipher letter from a keyed alphabet. Because the groups rarely line up with single letters, each cipher letter blends parts of its neighbours.

Why are there exactly 26 groups?

After the message is in Morse, only three symbols are used: dot, dash, and the separator x. Reading three at a time gives 3 × 3 × 3 = 27 combinations. The all-separator group xxx can never appear, because a run of separators is at most a double xx between words, which leaves 26 — one for every letter of the alphabet, with none spare and none missing.

What does the keyword do?

The keyword mixes the row of cipher letters that sits under the 26 trigraphs. Its unique letters are written first, then the rest of the alphabet in order, exactly like a keyed substitution alphabet. The trigraphs themselves stay in their fixed order. With no keyword the table is just A–Z, so the keyword is the shared secret that both sender and receiver must use.

Can you show a worked example?

With no keyword, SOS becomes the Morse stream dot-dot-dot x dash-dash-dash x dot-dot-dot. That is eleven symbols, so one x is added to make twelve. Read in threes the groups are (dot-dot-dot), (x dash-dash), (dash x dot), (dot-dot x), which on the plain A–Z table map to A, W, P, C. So SOS encrypts to AWPC.

How do I decode a Fractionated Morse message?

Reverse the steps: look up each cipher letter to get its three-symbol group, join the groups into one dot-dash-x string, split it on the separators (single x between letters, double xx between words), and read each run of dots and dashes back through the Morse table. In this tool, choose Decode and enter the same keyword that was used to encode.

Why is the padding done with x and not a dot or dash?

If the Morse stream is not a multiple of three symbols, the end is padded so the last group is complete. Padding with x works because x is a separator: trailing separators simply mark the end of the final letter or word and vanish when the message is decoded. Padding with a dot or dash would instead be read back as a real Morse symbol and could add a spurious extra letter.

Does it handle numbers and punctuation?

Letters and digits are encoded, because both have standard Morse codes. Punctuation and other symbols are dropped, and any run of spaces becomes a single word break. This means a contraction like "it's" is treated as the single word ITS, which matches the common reference implementations of the cipher.

What are trigraphs?

A trigraph here is simply a group of three Morse symbols — each one a dot, a dash, or the separator x. There are 26 of them once the impossible xxx is excluded, and they are always listed in the same fixed order. The cipher's only secret is which letter is assigned to each trigraph, which is what the keyword controls.

How is this different from plain Morse code?

Plain Morse just replaces each letter with dots and dashes, so anyone who knows Morse can read it instantly and the letter rhythm is plain to see. Fractionated Morse adds two more steps — grouping the Morse into threes and substituting each group with a keyed letter — so the output is ordinary-looking letters and the Morse structure is scrambled across the message.

Is the Fractionated Morse cipher secure?

No. The fractionation defeats simple frequency counting, but the underlying Morse leaves strong statistical patterns, and the cipher falls to classical solving methods and to computers, especially when the keyword is guessed or reused or when plenty of cipher text is available. It is excellent for puzzles and learning, but for real protection use a modern algorithm such as AES.

Is my text uploaded to a server?

No. All encoding and decoding happens entirely in your browser, so your text is never uploaded, logged, or stored. Even a share link keeps your text and keyword in the part of the URL after the # symbol, which browsers never send to a server, so your message stays private until you choose to share the link.

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